luteal phase

What are your ladies luteal phase. I have a 27/28 day cycle. My due date was July 4th dated by ultrasound tech but then my doctor came in and told me she's changing it to July 2nd because the baby I guess measure bigger than she thought. So if my due date is July 2nd and I put it in a conceiving calculator it says I ovulated on October 9nth which is when I had sex.lol. My last period was September 29th so that would mean my luteal phase is 18 days right ? .. I know it's hard to tell. I've always been curious to how long mine is.